1. Field of the Invention
The present invention relates to apparatus for use in cementing any tubular member that is run or landed with a string of drill pipe.
2. Description of the Prior Art
Prior art liner cementing equipment includes a flapper or a float valve at the bottom of the liner. The flapper is conventionally held open by a breakable plastic tab which is actuated (i.e., broken) by a drop ball when the cementing operation is to begin. Since the drop ball which is used to activate the float valve must be small enough to pass through the drill string, the maximum float valve opening size for a 13xe2x85x9cxe2x80x3 liner may be on the order of 2 to 3xe2x80x3 in diameter. As the liner is lowered into the well bore, the fluid in front of the liner must be displaced to flow through the bottom opening in the float valve as well as around the outside annulus defined by the well bore and the liner.
Two problems exist with respect to conventional cementing apparatus. First, the flow resistance of two above-identified flow paths may be high and thus cause a pressure buildup below the liner. This pressure buildup can: (a) cause damage to the formation; (b) result in loss of expensive drilling fluid; and (c) result in the liner sticking against the side of the borehole, which means that the liner does not go to the bottom of the hole. Second, the small opening through the float valve may, and often does, become plugged with cuttings and contaminants due to its small size and the highly contaminated environment in which it is used.
U.S. Pat. No. 5,960,881, which is incorporated herein by reference, discloses a downhole surge pressure reduction system to reduce the pressure buildup while running in liners. The system is typically located immediately above the top of the liner. Nonetheless, any plugging of the float valve at the lower end of the liner can, and very well may, render the surge pressure reduction system of the ""881 patent ineffective.
The method and apparatus according to the present invention overcomes the plugging problem which has heretofore existed.
In accordance with the present invention, a tubular member is provided that includes a landing collar which is attached at the bottom of the tubular member and which has an opening therethrough. This apparatus greatly reduces the likelihood of plugging the tubular member while running in and provides for lower flow resistance of fluid entering the tubular member during lowering in the hole.
An embodiment of the present invention also includes a lower liner wiper plug and an upper liner wiper plug. The upper liner wiper plug is releasably suspended from the drill string and the lower liner wiper plug is releasably suspended from the upper liner wiper plug. The lower liner wiper plug has at least one, and preferably two float valves. Both of these wiper plugs are thus near the top of the tubular member as the tubular member is run into the borehole.
Once the tubular member has been lowered to fall depth and the casing hanger has been set, the lower liner wiper plug is released from the upper liner wiper plug. Once released, the lower plug is pumped downhole by drilling fluid and thus displaces drilling mud from the bore of the tubular member through the large opening in the landing collar at the bottom of the tubular member. The lower liner wiper plug is locked into the landing collar, which results in float valves in the lower liner wiper plug being actuated. After cement has been pumped into the tubular member, the upper liner wiper plug is released from the drill string. As the upper liner wiper plug is pumped down, it forces the cement through the float valves, through the opening in the landing collar and into the annulus between the tubular member and the borehole.